A zero drop is not enough to notably alter the biomechanics of running in a cushioned shoe but may affect injury risk in some runners, according to research from Luxembourg presented at the IOC World Conference on Prevention of Injury and Illness in Sport, held in Monaco in March.
The findings suggest that, although barefoot running by definition involves a zero drop from the heel to the toe, other design features may play a bigger role in determining the extent to which minimalist running shoes are associated with barefoot-like gait.
Investigators from the Luxembourg Institute of Health randomized 553 runners to six months of running while wearing one of three experimental cushioned shoe styles that differed only in terms of shoe drop: 0, 6, or 10 mm. The zero-drop shoes had a 21-mm cushion in both the toe and heel.
Gait was assessed in a subset of 59 participants at baseline and after five months or 500 km as they ran on a treadmill at a self-selected speed. Changes from baseline did not differ significantly between groups for any of the gait variables measured except for knee abduction angle at midstance, which decreased by 1° in the zero-drop group but increased by 1° in the 6-mm group and by .7° in the 10-mm group.
Although the changes over time were statistically significant, they were still very small in magnitude, noted Daniel Theisen, PhD, head of the Sports Medicine Research Laboratory at the Luxembourg Institute of Health, who presented the biomechanics outcomes in Monaco.
“We have to ask if this [knee abduction] is clinically meaningful at all, and I’m not so sure,” Theisen said.
However, methodological aspects of the study may have affected the outcomes, he noted.
“We looked at shoe drop influence for normally cushioned shoes. It might be different if the zero-drop shoes were actually barefoot-like,” Theisen said. “[Also] this is not a within-subject comparison for different shoe models; we compared different groups wearing different shoes. This may make it more difficult to see results.”
In addition to the subgroup gait analysis, the researchers also followed up with all of the study participants with regard to injuries sustained during six months of running in the experimental shoes. For the group overall, shoe drop was not significantly associated with injury risk.
However, in occasional runners (those who said they had fewer than six months of regular running practice in the year prior to the study) shoes with a drop of 0 or 6 mm were associated with a lower injury risk than shoes with a 10-mm drop (hazard ratio [HR] = .48). And in those who ran more regularly, the two lowest shoe drop categories were associated with a higher injury risk than the 10-mm shoes (HR = 1.67).
“It seems safe to recommend low-drop shoes for occasional runners but not regular runners,” said Laurent Malisoux, PhD, a researcher at the institute, who presented the injury risk findings in Monaco.
Malisoux L, Chambon N, Urhausen A, Theisen D. Is shoe drop a key factor for injury prevention in running? Part 1: An RCT on injury risk. Br J Sports Med 2017;51(4):355.
Theisen D, Gette P, Chambon N, et al. Is shoe drop a key factor for injury prevention in running? Part 2: An RCT on running biomechanics. Br J Sports Med 2017;51(4):393-394.